Messages in this thread | | | Date | Sat, 22 Mar 2003 17:02:47 +0100 | From | Manfred Spraul <> | Subject | Re: [RFC] O(1) proc_pid_readdir |
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Ingo Molnar wrote:
>On Sun, 16 Mar 2003, Manfred Spraul wrote: > > > >>Below is a proposal to get rid of the quadratic behaviour of >>proc_pid_readir(): Instead of storing the task number in f_pos and >>walking tasks by tasklist order, the pid is stored in f_pos and the >>tasks are walked by (hash-mangled) pid order. >> >> > >have you seen my "procfs/procps threading performance speedup" patch? It >does something like this. > > The implementation is flawed:
>+static int get_pid_list(int index, int *pids, struct file *filp) > { >- struct task_struct *p; >- int nr_pids = 0; >+ int nr_pids = 0, pid = 0, pid_cursor = (int)filp->private_data; >+ struct task_struct *g = NULL, *p = NULL; > >- index--; > read_lock(&tasklist_lock); >- for_each_process(p) { >- int pid = p->pid; >- if (!pid) >- continue; >+ if (pid_cursor) { >+ p = find_task_by_pid(pid_cursor); >+ g = p->group_leader; >+ } >+ if (!p) { >+ g = p = &init_task; >+ index--; >+ } else >+ index = 0; >+ >+ goto inside; >+ >+ __do_each_thread(g, p) { > if (--index >= 0) > continue; >- pids[nr_pids] = pid; >+ pid = p->pid; >+ if (!pid) >+ BUG(); >+ if (p->tgid != p->pid) >+ pids[nr_pids] = -pid; >+ else >+ pids[nr_pids] = pid; > nr_pids++; > if (nr_pids >= PROC_MAXPIDS) >- break; >- } >+ goto out; >+inside: >+ ; >+ } while_each_thread(g, p); >+out: >+ filp->private_data = (void *)pid; > read_unlock(&tasklist_lock); >+ > return nr_pids; > } > > get_pid_list stores up to 20 pids in an array, and the last pid in the array is stored in filp->private_data, for the next call.
> int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir) > { >- unsigned int pid_array[PROC_MAXPIDS]; >+ int pid_array[PROC_MAXPIDS]; > char buf[PROC_NUMBUF]; > unsigned int nr = filp->f_pos - FIRST_PROCESS_ENTRY; > unsigned int nr_pids, i; >@@ -1192,14 +1217,16 @@ int proc_pid_readdir(struct file * filp, > nr++; > } > >- nr_pids = get_pid_list(nr, pid_array); >+ nr_pids = get_pid_list(nr, pid_array, filp); > > for (i = 0; i < nr_pids; i++) { >- int pid = pid_array[i]; >+ int pid = abs(pid_array[i]); > ino_t ino = fake_ino(pid,PROC_PID_INO); > unsigned long j = PROC_NUMBUF; > > do buf[--j] = '0' + (pid % 10); while (pid/=10); >+ if (pid_array[i] < 0) >+ buf[--j] = '.'; > > if (filldir(dirent, buf+j, PROC_NUMBUF-j, filp->f_pos, ino, DT_DIR) < 0) > break; > > But: proc_pid_readdir() doesn't use all 20 pids: It may return early if the user space buffer is full. Then your patch skips a few threads. Attached is my test app:
./getdents /proc 0 24 returns just 3 threads, ./getdents /proc 0 4000 returns (probably) all: 66 threads or processes.
-- Manfred /* * gendents.cpp: getdents tester. * * Copyright (C) 1999, 2001, 2003 by Manfred Spraul. * All rights reserved except the rights granted by the GPL. * * Redistribution of this file is permitted under the terms of the GNU * General Public License (GPL) version 2 or later. * $Header: /pub/home/manfred/cvs-tree/getdents/getdents.cpp,v 1.2 2003/03/22 16:01:34 manfred Exp $ */
#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <linux/types.h> #include <linux/dirent.h> #include <linux/unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <errno.h>
#define BUFSZ 131072 unsigned char entries[BUFSZ];
#define _syscall3(type,name,type1,arg1,type2,arg2,type3,arg3) \ type name(type1 arg1,type2 arg2,type3 arg3) \ { \ long __res; \ __asm__ volatile ("int $0x80" \ : "=a" (__res) \ : "0" (__NR_##name),"b" ((long)(arg1)),"c" ((long)(arg2)), \ "d" ((long)(arg3))); \ __syscall_return(type,__res); \ }
_syscall3(int, getdents, uint, fd, struct dirent *, dirp, uint, count);
static void hexdump(unsigned char* array, int len) { int i; for(i=0;i<len;i++) { if ((i%16) == 0) printf("\n%03x:", i); if((i%16)==8) printf(":"); printf("%02x ",(unsigned)array[i]); } printf("\n"); }
int main(int argc, char **argv) { int fd, retval, bufsz; printf("GETDENTS <dir> <offset> [<bufsz>]\n"); if (argc < 3 || argc > 4) return 1; fd = open(argv[1],O_RDONLY); if (fd < 0) { printf("open failed, errno %d.\n", errno); return 2; } if (argc == 4) bufsz = atoi(argv[3]); else bufsz = BUFSZ; lseek(fd, atoi(argv[2]), SEEK_SET); for(;;) { int offset = 0;
retval = getdents(fd, (struct dirent *)entries, bufsz); printf("retval is %d.\n", retval); if (retval <= 0) break; while (offset < retval) { struct dirent *walk = (struct dirent *)(&entries[offset]); // printf("dirent: %lxh.\n", (unsigned long)walk); // printf("dirent->d_ino = %ld.\n", walk->d_ino); // printf("dirent->d_off = %ld.\n", walk->d_off); // printf("dirent->d_reclen = %ld.\n", walk->d_reclen); printf("dirent->d_name = '%s'@%ld\n", walk->d_name, walk->d_off); offset += walk->d_reclen; } } return 0; }
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